Ceramic-metal composite assembly

ABSTRACT

A ceramic-metal composite assembly includes an intermediate member made of a material having a thermal expansion efficiency between those of the materials forming a ceramic member and a metallic shaft member. The intermediate member is metallurgically joined to the ceramic member whilst being mechanically joined to the metallic member to constitute a single unit.

This application is a divisional of application Ser. No. 07/987,186filed Dec. 8, 1992.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a ceramic-metal composite unit orassembly such as a ceramic turbocharger rotor, ceramic gas-turbinerotor, ceramic heating element, ceramic sensor, or the like which isused at a high temperature.

2. Disclosure Information

In recent years, ceramics have increasingly been used in various fieldsby the excellence of heat resistance, strength against thermal shock,mechanical strength at a high temperature, wear resistance, insulation,etc. However, the ceramics are not used alone but together with othermaterials such as metal so that they can show their excellent qualities.

An investigation has hereinbefore been made on how to unite a ceramicmember and a metallic member with a view to obtaining a single unit orassembly having a high joint strength. This is because when the ceramicmember and the metallic member are simply brazed together to constitutea single unit residual stresses are caused at the ceramic-metal jointportion due to the difference in thermal expansion efficiency betweenthe ceramic material and the metallic material, thus causing decrease ofthe joint strength and therefore making it impossible to attain asufficiently large joint strength.

This problem is pronounced when such a composite assembly is used at ahigh temperature.

To solve such a problem, it has been proposed to join a ceramic memberand a metallic member by press fitting as disclosed in Japanese PatentProvisional Publication No. 62-191478.

To the same end, it has also been proposed to fit a ceramic member in ametallic member and fill the clearance between them by silver solder forthereby joining them together as disclosed in Japanese PatentProvisional Publication No. 2-149477.

In either of such prior art structures, the metallic member is made ofan alloy such as Incoloy 903, having a low thermal expansion efficiencyand consisting of Fe--Ni--Co alloy and precipitation hardening elementsas Ti, Nb, Al, etc. However, by the use of such an alloy only, afavorable result cannot be attained. This is because there is aconsiderable difference in thermal expansion efficiency between theceramic member and the metallic member, that is, the thermal expansionefficiency of Incoloy 903 used for forming the metallic member is forexample 2.1 (×10⁻⁶ /° C.) at 30˜400° C., whilst the thermal expansionefficiency of silicon nitride used for forming the ceramic portion is8.2 (×10⁻⁶ /° C.) at 30˜400° C.

As a result, when either of such prior art composite assemblies is usedat a high temperature, the metallic member is expanded more than theceramic member to make it impossible to retain a sufficient interferencetherebetween, thus causing a problem that the joint strength is loweredand in some case the ceramic member can be dropped off from the metallicmember.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a ceramic-metalcomposite assembly which has a sufficiently large joint strength evenwhen it is used at a high temperature.

It is a further object of the present invention to provide aceramic-metal composite assembly of the above described character whichhas a sufficiently large interference at the ceramic-metal joint portioneven when it is used at a high temperature.

It is a further object of the present invention to provide aceramic-metal composite assembly of the above described character whichis suited for adoption to a turbocharger rotor.

According to the present invention, there is provided a ceramic-metalcomposite assembly which comprises a ceramic member, a metallic member,and an intermediate member having a thermal expansion efficiency betweenthose of the ceramic member and the metallic member, in which theintermediate member is chemically or metallurgically joined to theceramic member whilst being mechanically joined to the ceramic member.

The metallurgical joining means for joining the ceramic member and themetallic member together can be brazing, diffusion joining or welding,joining by the use of oxide, friction welding, hot pressing, hotisostatic pressing, etc. More specifically, brazing by the use of anactive brazing metal selected from the group of metals consisting ofAG--Cu--Ti alloys, Cu--Ni--Ti alloys, Cu--Ti alloys, joining by heatingby the use of a mixture of ceramic materials including Al₂ O₃, TiO₂,SiO₂, etc. and hot pressing by interposing between the joining portionsa metal selected from the group of metals consisting of Fe--Ni--Cralloys, Ni--Cr--Si alloys, Ni--Cr alloys and Nb are more desirable forsuch a metallurgical joining means.

The mechanical joining means for joining the metallic member and theintermediate member together can be press fitting, shrink fitting andfastening with bolts or screws.

While the material for the metallic member can be a material of lowthermal expansion efficiency such as carbon steel, alloy steel, heatresisting steel, stainless steel, Incoloy 903 or all of structuralmaterials such as heat resisting alloys, Ni alloys, Cu alloys, it ismore desirable such a material having a thermal expansion efficiencyclose to that of the intermediate member since the composite assemblycan have a larger joint strength.

The material for the intermediate member is selected on the basis of anoptional combination of a ceramic material and a metallic material whichare selected from the above described materials, in such a manner thatits thermal expansion efficiency is between those of the ceramicmaterial and the metallic material. For example, it can be either aceramic material or a metallic material such as W alloys, super hardalloys, composite material of Si3N4--TiN, Incoloy 903.

In this instance, shown in Table 1 are the thermal expansionefficiencies of the ceramic member, intermediate member and metallicmember, and shown in Table 2 are desirable combinations thereof. In themeantime, those materials can be selected variously for constitutingvarious combinations and therefore each cannot be limited to one of theceramic member, metallic member and the intermediate member.

                  TABLE 1    ______________________________________                                 Thermal Expansion    Sample                       efficiency (×10.sup.-6 /°C.)    No.    Material Composition  30˜400° C.                                         30˜700° C.    ______________________________________    1      silicon  10 wt % of Al.sub.2 O.sub.3,                                 2.1     2.6           nitride  Y.sub.2 O.sub.3 ; the                    remainder is                    Si.sub.3 N.sub.4    2      alumina  5 wt % of SiO.sub.2,                                 7.0     7.7                    CaO, MgO; the                    remainder is                    is Al.sub.2 O.sub.3    3      silicon  30 wt % of TiN;                                 2.8     3.8           nitride- the remainder           TiN      is Si3N4    4      Incoloy  38 wt % of Ni,                                 8.2     10.7           903      15 wt % of Co,                    0.7 wt % of Al,                    1.4 wt % of Ti,                    3 wt % of Nb;                    the remainder                    is Fe    5      W alloy  5 wt % of Fe, Ni;                                 5.1     5.4                    the remainder                    is W    6      supper   10 wt % of Co;                                 4.8     5.3           hard     the remainder           alloy    is WC    7      heat     JIS-SUH616   11.9    12.1           resisting           steel    8      alloy steel                    JIS-SNCM439  13.2    14.3    ______________________________________

                  TABLE 2    ______________________________________            Ceramic      Intermediate                                    Metallic    No.     member       member     member    ______________________________________    A       silicon nitride                         W alloy    alloy steel    B       silicon nitride                         super hard heat resisting                         hard alloy steel    C       silicon nitride                         silicon    stainless steel                         nitride-TiN    D       silicon nitride                         super hard Incoloy 903                         alloy    E       alumina      Incoloy 903                                    stainless steel    D       alumina      Incoloy 903                                    stainless steel    ______________________________________

In the meantime, since the intermediate member and the metallic memberare mechanically joined together, a metallic material is more desirablefor forming the intermediate member when selected from among thematerials having substantially the same thermal expansion efficiency.This is because the outer surface of the intermediate member made of ametallic material can be rough to some extent in assembly and thereforean increased flexibility in assembly is attained.

Further, the difference in thermal expansion efficiency between theintermediate member and the ceramic member is desirable to be equal toor smaller than 4×10⁻⁶ /° C. and further desirable to be equal to orsmaller than 3×10⁻⁶ /° C.

Further, while the method of joining the intermediate member and theceramic member has been described as above, an intermediate member madeof a soft metal such as Ni, Cu, Fe or an intermediate member made of aheat resisting soft metal such as Ni--Cu alloys may be interposedbetween the intermediate member and the ceramic member in accordancewith the necessity.

Such a ceramic-metal composite assembly can prevent decrease of thejoint strength at a high temperature since the intermediate member has athermal expansion efficiency between those of the ceramic member and themetallic member and can decrease the thermal stresses resulting when itis used at a high temperature.

Further, since the intermediate member is metallurgically joined withceramic member to constitute a united sub-assembly whilst theintermediate member and the metallic member are mechanically joinedtogether by interference fit, etc., a sufficient interference in aradial direction between the intermediate member and the metallic membercan be maintained even when each members are heated to expand since thedifference in thermal expansion efficiency between the intermediatemember and the metallic member is small. That is, a sufficientinterference can be retained at the time of usage of the compositeassembly at a high temperature, thus making it possible to preventdecrease of the joint strength with which the ceramic member andmetallic member are joined together.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of a ceramic-metal composite assemblyaccording an embodiment of the present invention;

FIG. 1B is a sectional view of the composite assembly of FIG. 1A;

FIGS. 2A-2C and 3A-3B are views for illustrating the method of producingthe composite assembly of FIG. 1;

FIG. 4 is a view for illustrating the method of testing the assembly ofFIG. 1; and

FIGS. 5 through 10 are sectional views of ceramic-metal compositeassemblies according to further embodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring first to FIG. 1, a ceramic-metal composite assembly accordingto an embodiment of the present invention mainly consists of a metallicmember 2 made of heat resisting steel (e.g. JIS-SUH 616), a ceramicmember 5 made of silicon nitride, and an intermediate member 6 made ofIncoloy 903. The metallic member 2 is hollow cylindrical to have a bore4. The ceramic member 5 has an outer diameter substantially equal to thediameter of the bore 4 and is integrally connected to the metallicmember 2 by way of the intermediate member 6 which is fitted in the bore4 of the ceramic member 2. The assembly 1 is provided with anintermediate layer 7 which is made of a soft metal and interposedbetween the ceramic member 3 and the intermediate member 6.

The ceramic member 5 and the intermediate member 6 are joined byheating, that is, joined chemically or metallurgically by way of theintermediate layer 7. On the other hand, the metallic member 2 and theintermediate member 6 are joined mechanically by press fitting theintermediate member 6 in the bore 4 of the metallic member 2. In brief,disposed between the ceramic member 5 having a smaller thermal expansionefficiency and the metallic member 2 having a larger thermal expansionefficiency is the intermediate member 6 having a thermal expansionefficiency intermediate between those of the metallic member 2 and theceramic member 5.

In the meantime, the dimensions of each members are shown in Table 3. Ofthe members, the metallic member 2 is made of JIS-SUH 616 and machinedafter quenching and tempering according to the Japanese Industrialstandards (JIS), whilst the intermediate member 6 be aged by heating ata temperature of 720° C. for 8 hours and at a temperature of 620° C. for8 hours.

                  TABLE 3    ______________________________________    Metallic member                   outer dia.: 16 mm, length: 25 mm,                   inner dia.: 9.94 mm (chamfering of                   bore end: C3.0 mm)    Ceramic member dia.: 11 mm, length: 20 mm (chamfering                   at an end: C1.0)    Intermediate member                   dia.: 11 mm, length: 5.0 mm    Intermediate layer                   dia.: 11 mm, thickness: 0.5 mm    ______________________________________

The method of producing such a composite assembly 1 will be describedwith reference to FIGS. 2A-2C and 3A-3B in which the different scalesare employed only for convenience of illustration.

Firstly, as shown in FIG. 2A, the intermediate layer 7 is formed betweenthe ceramic member 5 and the intermediate member 6. The intermediatelayer 7 is formed by laying one upon another and in the followingdescribed order from the ceramic member 5 side a Ti foil 7a of thethickness of 0.003 mm, a Cu foil of the thickness of 0.02 mm, a Ni plate7c of the thickness of 0.5 mm and a Cu foil 7d of the thickness of 0.02mm.

Then, the ceramic member 5 and the intermediate member 6 with theintermediate layer 7 being constructed and arranged in the above mannertherebetween are heated in the vacuum of 10⁻⁵ torr and at a temperatureof 1200° C. for 1 hour, so that the ceramic member 5 and theintermediate member 6 are joined to constitute a single unit or unitedsubassembly 10.

Then, the entire of the outer circumferential surface of the unitedsubassembly 10 is ground by the use of a diamond grinder so that theouter diameter of the united subassembly 10 is sized to 10 mm. Further,as shown in an enlarged scale in FIGS. 2B and 2C, an end of theintermediate member 6 is machined to have a chamfer of 1 mm and agradually slanted portion 12 slanted at an angle of 4' at a locationinside of the chamfer 11.

Further, as shown in FIG. 3A, the metallic member 2 which is hollowcylindrical is formed with a beveled portion 15 at an end of the bore 4so that the beveled portion 15 constitutes a guide opening 16 forinsertion of the integral unit 10 into the bore 4.

Then, as shown in FIG. 3B, the intermediate member 6 of the subassembly10 is press fitted by 3 mm in length into the metallic member 2 throughthe guide opening 16 at a speed of 0.5 mm/min. to constitute the unitedassembly 1 shown in FIG. 1.

The united assembly 1 of this embodiment produced in this manner issmall in the difference in thermal expansion efficiency between theintermediate member 6 and the metallic member 2 and therefore can retaina sufficient interference at a high temperature and therefore can attaina large joint strength. Accordingly, the assembly 10 is superior indurability to a comparable prior art assembly and has such a jointstrength that is large enough to enable production of a large-sizedcomposite assembly.

Then for assuring the effect of this embodiment description will be madeto test sample.

Various test samples made of different materials were prepared andtested for a dropping-off load at a high temperature in order to examinethe joint strength of the composite assembly 1 of this embodiment.

The measurement of the dropping-off load were made by first placing, asshown in FIG. 4, the ceramic member 5 of the composite assembly 1 insideof an annular block 19 whilst allowing the metallic member 2 to abutupon the upper surface of the annular block 19, then pushing thesubassembly 10 downward at a loading speed of 0.5 mm/min. and measuringthe load by which the subassembly 10 were dropped off from the metallicmember 2. The result of measurements is shown in Table 4.

Further, such comparative examples were prepared in which nointermediate member was used but the metallic member and the ceramicmember were directly joined together by press fitting to constitute anassembly of 25 mm in length though the ceramic member and metallicmember were made of the same materials with those of the above describedembodiments. The result of measurement is shown in Table 4.

                  TABLE 4    ______________________________________    Test    sample Ceramic    Metallic Intermediate                                        Dropping-off    No.    member     member   member   load (kgw)    ______________________________________    Samples of this invention    1      silicon    W alloy  SUH616   300 and more           nitride           (10 wt % of           Al.sub.2 O.sub.3, Y.sub.2 O.sub.3 ;           the remainder           is Si.sub.3 N.sub.4)    2      silicon    W alloy  Incoloy 903                                        300 and more           nitride    3      silicon    super    SUH616   300 and more           nitride    hard                      alloy    4      silicon    Si3N4-   Incoloy 903                                        240           nitride    0TiN    Comparative examples    5      silicon    not      Incoloy 903                                        140           nitride    provided    6      silicon    not      SUH616   0           nitride    provided    ______________________________________

In the above table 4, the ceramic member is made of silicon nitrideconsisting of 10 wt % of Al₂ O₃, Y₂ O₃ and the remainder of Si₃ N₄.SUH616 is a heat resisting steel whilst being a material for quenchingand tempering. Incoloy is a material for hardening by aging.

As will be apparent from Table 4, the composite assembly of thisinvention has a large dropping-off load of 240 Kgw and is thereforedesirable since it can obtain a large joint strength at a hightemperature, whilst the comparative examples have a small dropping-offload of 140 Kgw and is therefore undesirable.

FIG. 5 shows a ceramic-metal composite rotor 20 for a turbochargeraccording to a further embodiment of the present invention. The rotor 20includes a ceramic turbine wheel 21 made of silicon nitride and having astub shaft 21a, an intermediate member 22 made of W alloy and joined tothe stub shaft 21a of the ceramic wheel 21 by way of a Ni plate 23 toconstitute a united subassembly 24, and a metallic member 25 having asocket portion 26 in which the intermediate member 22 of the subassembly24 is fitted. In the meantime, the socket portion 26 of the metallicmember 25 has a wall surrounding the stub shaft 21a of the ceramicturbine wheel 21 and having an annular recess 27 so as not to directlycontact the stub shaft 21a, i.e., so as to provide a space between thewall of the socket portion 26 and the stub shaft 21a.

In production of the ceramic-metal composite rotor 20, the turbine wheel21 and the intermediate member 22 of 10 mm in diameter with a Ni plate23 being interposed between the stub shaft 21a and the intermediatemember 22 are joined by heating to constitute the subassembly 24. On theother hand, the metallic member 25 made of heat resisting steel(JIS-SUH616) is treated by a predetermined quenching and temperingprocess so as to be as hard as HRC 34 and is formed with the socketportion 26 of 9.94 mm in inner diameter. The intermediate member 22 ofthe subassembly 24 is press fitted in the socket portion 26 of themetallic member 25 to constitute the composite rotor 20.

The composite rotor 20 was installed in a turbine housing and subjectedto a rotation test in which it was rotated at a speed of 100,000 rpm andat an exhaust gas temperature of 950° C. for 50 hours. By this test, afavorable results was obtained, i.e., no cracks or breakage and nomovements at the joining portions were found.

FIG. 6 shows a ceramic-metal composite rotor 30 according to a furtherembodiment though its lower half is omitted for convenience ofillustration. This embodiment differs from the previous embodiment ofFIG. 5 in the material forming the intermediate member 31. Theintermediate member 31 is made of a super hard alloy which has a littersmaller thermal expansion efficiency than W alloy. The intermediatemember 31 is joined to the turbine wheel 33 by way of the Ni platewhilst being press fitted in the metallic member 34.

Accordingly, this embodiment can produce substantially the same effectwith the previous embodiment of FIG. 5.

FIG. 7 shows a ceramic-metal composite rotor 40 according to a furtherembodiment. The turbocharger rotor 40 differs from the previousembodiment of FIG. 6 in that an annular recess 41 is not provided to themetallic member 42 but to the subassembly 46 made up of a turbine wheel43, Ni plate 44 and an intermediate member 45.

This embodiment can produce substantially the same effect to theprevious embodiments of FIGS. 5 and 6.

FIG. 8 shows a ceramic-metal composite rotor 50 according to a furtherembodiment. This embodiment is substantially similar to the previousembodiment of FIG. 7 except that the metallic member 51 consists of asocket portion 51a formed with a socket recess 52 and made of Incoloy903 and a shaft portion 51b made of alloy steel (JIS-SNCM439).

To obtain the metallic member 51, the socket portion 51a is first joinedto the shaft portion 51b by friction welding and then aged by heating ata temperature of 720° C. for 8 hours and at a temperature of 620° C. for8 hours. Thereafter, the shaft portion 51b is hardened by high-frequencyinduction hardening. Finally, the socket portion 51a is finished tocomplete the metallic member 51.

This structure enables usage of the rotor 50 at a higher temperaturethan the previous embodiment of FIG. 7 since the difference in thermalexpansion efficiency between the intermediate member 53 and metallicmember 51 is small. Except for this, this embodiment can producesubstantially the same effect to the previous embodiment of FIG. 7.

FIG. 9 shows a ceramic-metal composite rotor 60 according to a furtherembodiment of the present invention. This embodiment is substantiallysimilar to the previous embodiment of FIG. 8 except that the metallicmember 61 consists of a socket portion 61a formed with a socket recess62 and made of Incoloy 903 and a shaft portion 61b made of alloy steel(JIS-SNCM439), which socket portion 61a and shaft portion 61b are joinedtogether by electron beam welding. The shaft portion 61b has an endextending through the socket portion 61a to partially define the bottomof the socket recess 62.

This embodiment can produce substantially the same effect to theprevious embodiment of FIG. 8.

FIG. 10 shows a ceramic-metal composite rotor 70 according to a furtherembodiment. This embodiment is substantially similar to the previousembodiment of FIG. 5 except that the subassembly 71 consists of aturbine wheel 72 made of silicon nitride, Ni plate 73, a compositematerial plate made of Si3N4-30TiN and an intermediate member 76 made ofW alloy.

This embodiment makes it possible to use the rotor 70 at a highertemperature than the previous embodiment of FIG. 5 since the compositematerial plate 74 has a thermal expansion efficiency between those ofthe silicon nitride and W alloy.

What is claimed is:
 1. A ceramic-metal composite assembly comprising:(A)a ceramic member; (B) a metallic member; and (C) an intermediate membermade of a material having a thermal expansion efficiency between thoseof the materials forming said ceramic member and said metallic member;said intermediate member being metallurgically joined to said ceramicmember whilst being mechanically joined to said metallic member.
 2. Aceramic-metal composite assembly comprising:(A) a ceramic member; (B) ametallic member; (C) an intermediate member made of a material having athermal expansion efficiency between those of the materials forming saidceramic member and said metallic member; said intermediate member beingjoined to said ceramic member whilst being joined to said metallicmember; (D) metallurgical joining means for joining said intermediatemember to said ceramic member; and (E) mechanical joining means forjoining said intermediate member to said metallic member.
 3. Aceramic-metal composite assembly according to claim 2, wherein saidmetallurgical joining means comprises brazing by the use of an activebrazing metal selected from the group of metals consisting of Ag--Cu--Tialloys, Cu--Ni--Ti alloys and Cu--Ti alloys.
 4. A ceramic-metalcomposite assembly according to claim 2, wherein said metallurgicaljoining means comprises heating by the use of a mixture of ceramicmaterials selected from the group consisting of Al₂ O₃, TiO₂ and SiO₂.5. A ceramic-metal composite assembly according to claim 2, wherein saidmetallurgical joining means comprises hot pressing by interposingbetween said intermediate member and said ceramic member a metalselected from the group of metals consisting of Fe--Ni--Cr alloys,Ni--Cr--Si alloys, Ni--Cr alloys and Nb.
 6. A ceramic-metal compositeassembly according to claim 2, wherein said mechanical joining meanscomprises press fitting.
 7. A ceramic-metal composite assembly accordingto claim 2, wherein said mechanical joining means comprises shrinkagefitting.
 8. A ceramic-metal composite assembly according to claim 2,wherein said material forming said intermediate member is selected fromthe group of metals and ceramics consisting of W alloys, super hardalloys, Si₃ N₄ -Ti composite material and Incoloy
 903. 9. Aceramic-metal composite assembly as claimed in claim 2, wherein saidmechanical joining means (E) is selected from the group consisting ofpress fitting, shrink fitting and fastening with bolts or screws.
 10. Aceramic-metal composite assembly as claimed in claim 2, wherein saidceramic member (A) is made of a ceramic material selected from siliconnitride and alumina.
 11. A ceramic-metal composite assembly as claimedin claim 2, wherein said metallic member (B) is made of a materialselected from the group consisting of alloy steel, heat resisting steel,stainless steel and Incoloy
 903. 12. A ceramic-metal composite assemblyas claimed in claim 2, wherein said intermediate member (C) is made of amaterial selected from the group consisting of tungsten alloy, superhard alloy, silicon nitride-TiN and Incoloy
 903. 13. A ceramic-metalcomposite assembly comprising:(A) a shaft member made of a ceramicmaterial; (B) an intermediate member made of a metallic material andjoined to an end of said shaft member by metallurgical joining means;and (C) a hollow cylindrical member made of a metallic material, fittedon said intermediate member and joined to said intermediate member bymeans of mechanical joining means; wherein said metallic materialforming said intermediate member has a thermal expansion efficiencybetween those of the materials forming said shaft member and said hollowcylindrical member.
 14. A ceramic-metal composite assembly according toclaim 13, wherein said shaft member is made of a material consisting ofSi₃ N₄, said hollow cylindrical member is made of heat resisting steel,and said intermediate member is made of Incoloy
 903. 15. A ceramic-metalcomposite assembly according to claim 14, wherein said metallurgicaljoining means comprises heating said shaft member and said intermediatemember in a vacuum while interposing therebetween an intermediate layerconsisting of foils of Ti and Cu and a sheet of Ni.
 16. A ceramic-metalcomposite assembly according to claim 15, wherein said mechanicaljoining means comprises press fitting.